1. Field of the Invention
The present invention relates to a light-emitting device and a manufacturing method of the light-emitting device.
2. Description of the Related Art
A light-emitting element using an organic compound as a luminous body, which has characteristics such as thinness, lightness in weight, high-speed response, and DC drive at low voltage, is considered to be applied to a next-generation flat panel display. In particular, a display device in which light-emitting elements are arranged in matrix is considered to have an advantage in a wide viewing angle and excellent visibility over a conventional liquid crystal display device.
It is said that, as for a light-emitting mechanism of the light-emitting element in which a layer containing an organic compound (hereinafter, referred to as an organic compound layer) is used as a light-emitting layer, voltage is applied between a pair of electrodes where an organic compound layer is interposed, and thus electrons injected from a cathode and holes injected from an anode are recombined in the organic compound layer to form molecular excitons, and the molecular excitons release energy when returning to a ground state, whereby light is emitted. Singlet excitation and triplet excitation are known as excited states, and it is thought that light emission can be achieved through either of the excited states.
An organic compound layer included in a light-emitting element includes at least a light-emitting layer. In addition, the organic compound layer can have a stacked-layer structure including a hole injecting layer, a hole transporting layer, an electron transporting layer, an electron injecting layer, and/or the like, in addition to the light-emitting layer.
Although a light-emitting layer can be formed of only a light-emitting material, it is known that the light-emitting layer is formed of a combination of a host material and a dopant material so that desired characteristics of emission wavelength, emission efficiency, and the like are obtained. For example, the present applicant discloses a light-emitting element containing a host material and a dopant material in Patent Document 1 (Japanese Published Patent Application No. 2004-288439).
In addition, an EL material for forming an organic compound layer is broadly classified into a low molecular (monomer) material and a high molecular (polymer) material. A low molecular material is generally evaporated using an evaporation apparatus. A conventional evaporation apparatus, in which a substrate is set on a substrate holder, includes a crucible (or a deposition boat) in which an EL material, that is, an evaporation material is contained; a shutter for preventing the EL material to be sublimated from rising; and a heater for heating the EL material in the crucible. Then, the EL material which is heated by the heater is sublimated, whereby the EL material is evaporated over the substrate. For example, the present applicant discloses a evaporation apparatus which is capable of moving an evaporation source relative to a substrate in Patent Document 2 (Japanese Published Patent Application No. 2004-043965).